The present invention relates generally to vehicles and more particularly to heavy duty construction equipment such as a vehicle that has a crane supported on a turntable that is rotated about an axis on the frame for the vehicle. In vehicles of this type, the equipment is designed so that the turntable is rotated by some drive means with respect to the frame of the vehicle that is supported on wheels. These vehicles normally have some type of brake means associated with the turntable to lock the turntable with respect to the frame when the crane is being operated.
In the past, there have been two types of systems which have been utilized as manufacturers installed equipment for such vehicles. At the time of manufacture, the vehicle or crane is equipped with either a free swinging or an automatic swinging brake system. The automatic brake system incorporates a spring applied brake which is released by the hydraulic fluid that is utilized for operating the hydraulic swing motor. In this system, the pressure rise on either side of the hydraulic swing motor is delivered to the brake cylinder to release the brake and, when the swing control valve is returned to neutral, hydraulic oil is bled from the brake cylinder to cause the spring to apply the brake.
In the free swinging system, the brake is again a spring applied brake which is released by hydraulic pressure that is controlled manually through the use of a control valve.